Pal

Structure

Pal (peptidoglycan-associated lipoprotein) is a lipoprotein which is anchored in the outer membrane with an approximate length of 173 amino acids in the precursor form. It contains a signal sequence including an LVAC motif, with the flexible, hydrophobic N-terminal tail binding to the inner leaflet of the outer membrane and anchoring it. During translocation, signal peptidase II cleaves the LVAC motif, and the localisation of Pal is dependent on the Lol protein system. Serine, the amino acid at #2 position in the mature protein is a localisation determinant for the position of Pal in the outer membrane^[1]. The periplasmic domain of Pal can be seen in the 3D structure 1OAP.

Function

One of the roles of Pal is thought to be an anchor, linking the outer membrane to the peptidoglycan layer and offering support to this connection^[2]. It is also possible that Pal is involved in the translocation of subunits of the surface O-antigens, affecting its structure^[1].

Pal is also thought to play a significant role in the process of pathogenesis. The protein is highly immunogenic, which also makes them suitable candidates for the production of vaccines^[1].

Interactions of Pal

Directed deletion mutagenesis was carried out to investigate the interactions of Pal with different components of the Tol-Pal system^[3]:

1. Pal and the peptidoglycan layer - specific residues in the C-terminal domain including S126, G128 and R146 are responsible for the modification of the electric charge, and may be responsible for affecting the peptidoglycan interaction.
2. Pal and TolB - see TolB
3. Pal and TolA - Pal may play a role in the stabilisation of TolA, and that this interaction is essential if the cell integrity is to be maintained.